ABSTRACTS OF PAPERS ON THE BIOLOGY OF HAIR GROWTH 37 in the deformed cells this controls the direction of fibrils subsequently added. "THE NATURE OF HAIR PIGMENT" TttOM•S B. FITZPATRICK, PETER BRUNET AND ATSUSttI KUKITA Dept. of Derrnatology, University of Oregon, Portland, Oregon. The large variety of hair pigments has provided material on which naturalists, geneticists,, and biochemists have been able to carry out com- parative studies on the r, ature and control of pigmentation. Although superficial examination of hair would indicate a wide range of colour hues, microsqopic examination has re•ealed ,only three types of pigmented granules, namely, black, brown and yellow. , The study of the nature of hair pigment has proved generally unrewarding because it has not yet been possible to isolate pure fractions for chemical characterisation. Many of the advances on the nature of hair pigment have been made using the synthetic approach following the action of enzymes in the hair bulb on chromogenic substrates. But ultimately it xvill be nece'•ary to combine such a synthetic approach with chemical analysis of naturally occurring pigment. Differences in hair colour are biochemical differences and the genetic pattern of hair colour indicates that brown and black pigment is under the same genetic control, whereas, yellow (Pheomelanin) is under a different genetic control. Thus, two separate, but possibly interrelated, metabolic pathways of brown-black and yellow hair pigment are suggested. , Using a histochemical radioautographic technique and dl-tyrosine-2-C •4 as a substrate, it has been shown that the hair bulbs of mice incorporate tyrosine into pigment cells. The activity of tyrosinase is related to the stage of the hair cycle. In the C-57 black mouse, tyrosinase activity is not detect- able with the radioautographic technique during Anagen I and II, but appears weakly in Anagen iii and gradually increases in amount during Anagen IV, V and VI. Tyrosinase activity is absent during the Telogen stage of the hair cycle. The factors that regulate •the tyrosinase activity during the hair growth cycle are not known. It is possible, as suggested by Chase, that the cessation of tyrosinase activity iust prior to catagen may be related to the development of an inhibitor. The degree of incorporation of tyrosine-2-C •4 indicated by silver deposit in the radioautographs is very strong in intense brown mice (a/a b/b C/C D/D P/P) and in brown mice with Maltese dilution where d/d replaces D/D.' There is slightly less incorporation in both yellow mice (AY/• B/B C/C D/D P/P) and intense blacks (a/a B/B , C/C D/D P/P) and decreased but detectable incorporation in black mice with pink-eyed dilution, p/p replacing P/P of the intense blacks. Albinos showed

38 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS no uptake of labelled tyrosine. The ability to oxidise tyrosine is thus found in both melanic and pheomelanic follicles, melanic animals showing a greater activity than pheomelanic. It is quite clear at this time that black and brown. melanin appear to be closely related chemically, and genetical evidence indicates that their modes of formation are closely similar. Pheomelanin differs chemically from melanin, and genetical evidence indicates a very distinct mode of formation for the two pigments. Tyrosinase is involved in the formation of both melanin and pheomelanin, and tyrosine can be considered to be the precursor of melanin. While tyrosine will act as a substrate for ph•.omelanic hair follicles in vitro, the pigment formed is abnormal, and there is little or no indication that tyrosine is the natural chromogert of pheomelanin the oxidation of tyrosineby pheomelanic follicles may be involved only indirectly in pigment formation, and tyrosine (or its oxidation products) may not be the pigment precursor. The •ctivity of the genes for pheomelanin production in the guinea pig or the mouse "turn on" the production of pheomelanin in a very definite way no intermediates between melanin and pheomelanin appear to be formed. This clear-cut action of the genes presupposes a switch- mechanism, probably involving one enzymic step. The possible dual role of tyrosine and tryptophane intermediates in this switch-mechanism is suggested by the investigations of Butenandt, who showed that the formation of the red-yellow pigment, xanthomatin, depended on the conversion of dopa to dopa quinone in the presence of tyrosinase, and the non-enzymic oxidation of 3-hydroxykynurenin to xanthomatin by the dopa quinone which was reduced back to dopa. In some histochemical experiments using red human hair balbs and hair follicles of intense yellow, e/e, guinea pigs, we have demonstrated that melanin formation is absent in pheomelanic human and guinea pig hair follicles following incubation in dopa and 3-hydroxykynurenin in a molar ratio of 1: 4 for 20 hours. If the ratio of these substrates is 4:1 (dopa: 3-hydroxykynurenin) no black pigment is formed in four hours, but after 20 hours (all the 3-hydroxykynurenin having been oxidised) black pigment is found to have been deposited. These results provide necessary but not sufficient evidence for an explanation of pheomelanin formation as the result of the oxidation of an o-aminophenol by dopa quinone produced by the oxidation action of tyrosinase on dopa. It is compatible with the observation that pheomelanic hair follicles contain tyrosinase, and it would explain the pigmentary switch-mechanism leading either to melanin or pheomelanin, this being the result of the absence or presence of o-amino- phenol. The critical enzyme operating the switch could be one bringing about hydroxylation of an aromatic amine. The yellowish-brown pigments formed by the oxidation condensation of o-aminophenols are soluble, as is pheomelanin, in dilute alkali. Although no systematic search for trypto-